A chitosan-based multifunctional macromolecular rubber antioxidant with olefin groups, and its preparation method and application

Abstract

The present invention discloses a chitosan-based multifunctional macromolecular rubber antioxidant with alkenyl groups, and its preparation method and application. The present invention prepares a chitosan-based multifunctional macromolecular rubber antioxidant with alkenyl groups by first using an acid to form a salt with the active amino group on the chitosan to protect the amino group, then using the active hydroxyl group on the chitosan to react with an unsaturated fatty acid or an unsaturated fatty acid halide, and then using the active amino group on the deprotected chitosan to chemically react with a small molecule antioxidant containing a carboxyl group. The chitosan-based multifunctional macromolecular antioxidant provided by the present invention is not easy to volatilize, is green and environmentally friendly, and is resistant to migration. It can not only promote rubber vulcanization and significantly improve the thermal oxidative aging resistance and mechanical properties of rubber materials, but also has good compatibility with the rubber matrix. At the same time, it also has excellent extraction resistance and can exert a lasting anti-thermal oxidative aging effect on rubber materials.

Description

Technical Field

[0001] The invention belongs to the technical field of rubber additives, and particularly relates to an alkenyl-containing chitosan-based multifunctional macromolecular rubber antioxidant, a preparation method and application thereof. Background Art

[0002] Rubber is an important material indispensable to human life and social development. Rubber products such as tires, rubber shoes, seals, and conveyor belts are widely used in transportation, national defense, medical care, and daily necessities. Rubber additives generally refer to additives that help improve the processing properties and performance of rubber products. These mainly include rubber vulcanizers, vulcanization accelerators, vulcanization activators, rubber antioxidants, and rubber reinforcing agents. They are an indispensable component of rubber products. Due to the large number of unsaturated bonds in the rubber matrix, it is very susceptible to aging under conditions such as light, heat, oxygen, and ozone, causing deterioration in its performance and appearance, thereby shortening the service life of rubber products. Thermal oxidative aging of rubber materials is the most common form of aging. Adding rubber antioxidants can effectively delay the aging process of rubber materials, inhibit damage to the rubber material structure caused by aging, and extend its service life.

[0003] However, most traditional rubber antioxidants are small-molecule compounds. Due to their low molecular weight, they are prone to migration, volatility, poor resistance to solvent extraction, and low thermal stability during rubber processing and use, significantly reducing their anti-aging capabilities. Furthermore, the migration and diffusion of antioxidants can contaminate the surrounding environment and even enter the human body, posing a threat to human health. Furthermore, traditional antioxidants, with their single anti-aging effect, are no longer sufficient to meet the needs of today's rubber additive development. Multifunctional rubber additives meet the human demand for "multiple functions in one dose, conserving resources."

[0004] Compared to common small-molecule rubber antioxidants, macromolecular rubber antioxidants have become a research hotspot in the field of rubber additives due to their advantages such as low mobility, extraction resistance, good compatibility with rubber, and excellent thermal stability. Currently, there are two main methods for preparing macromolecular rubber antioxidants both domestically and internationally: one is a type of rubber antioxidant directly synthesized through polymerization using small-molecule additive monomers with anti-aging functional groups as raw materials. For example, Beer et al. used hydroxyl-functionalized terminal diene alkyl chains and 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid as raw materials. In the presence of dicyclohexylcarbodiimide (DCC) and 4-dimethylaminopyridine (DMAP) catalysts, they synthesized terminal diene antioxidant monomers through esterification. They then prepared macromolecular antioxidants with molecular weights ranging from 3000 to 5600 g / mol through polymerization. (Immobilization of antioxidants via ADMET polymerization for enhanced long-term stabilization of polyolefins. European Polymer Journal, 2013, 49(12): 4257-4264.); Shehata et al. used N-(4-hydroxyphenyl)acrylamide and N-(4-mercaptophenyl)acrylamide, which have similar structures, as monomers, AIBN as initiator, and THF as solvent to synthesize macromolecular antioxidants with phenolic hydroxyl and thiol structures by solution polymerization (Effect of Some Polymeric Phenolic Antioxidants on the Properties of SBR Vulcanizates. Polymer Plastics Technology & Engineering, 2005, 44(7): 1281-1295.). This type of macromolecular antioxidant generally has good migration resistance, extraction resistance, and high thermal stability, but the disadvantages are that the preparation conditions are relatively harsh, the process is relatively complex, and the yield is low. The second method is to use synthetic polymers or natural polymers as the matrix and introduce small molecule antioxidants into the polymer structure through chemical reactions to prepare large molecule antioxidants.For example, Wu et al. used isophorone diisocyanate (IPDI) as a bridging agent to bridge 2,2'-thiobis(4-methyl-6-tert-butylphenol) (TPH) to sulfide-containing polyhydroxy polybutadiene (PHPBT) to prepare a macromolecular antioxidant PHPBT-b-TPH. Although the anti-thermal oxidative aging performance of this macromolecular antioxidant is better than that of the corresponding small molecule bisphenol antioxidant, its anti-thermal oxidative aging ability is reduced, and the addition amount needs to be increased (Extraction resistance and mechanism of a macromolecular hindered phenol antioxidant in natural rubber. Journal of Applied Polymer Science, 2017, 134(22):44905(1-5).). Xie et al. used isophorone diisocyanate (IPDI) as a bridging agent to graft the small molecule antioxidant 2,6-di-tert-butyl-4-hydroxymethylphenol (DBHMP) onto the natural macromolecule β-cyclodextrin (β-CD) to prepare the macromolecular antioxidant β-CD-DBHMP (Synthesis of AStar-Shaped Macromolecular Antioxidant Based on-Cyclodextrin and its Antioxidative Properties in Natural Rubber. Macromolecular Materials and Engineering, 2015, 300(9):893-900.). This type of macromolecular antioxidant has better solvent extraction resistance than the corresponding small molecule phenolic antioxidant, but its resistance to thermal oxidative aging is not significantly improved.

[0005] Chitosan is a green, natural polymer material with abundant sources and low cost. Its structure contains -NH2 and -OH groups that can be modified, allowing for various functionalities to be imparted to chitosan through chemical modification. Our research group previously synthesized GMMP (2-tert-butyl-6-(3-tert-butyl-2-hydroxy-5-methylphenyl)methyl-4-methylphenyl acrylate) (GM) and mercaptopropionic acid (MPA) via a thiol-ene click reaction. GMMP was then grafted onto a low-molecular-weight chitosan oligosaccharide (COS) matrix using the reactivity of the carboxyl groups. This resulted in the successful preparation of a novel chitosan-based macromolecule antioxidant, COS-GMMP, for rubber / silica composites (Effects of a novel chitosan-based macromolecule antioxidant COS-GMMP on the thermo-oxidative aging of styrene-butadiene rubber / silica composites. Polymer Degradation and Stability, 2022, 195: 109813). COS-GMMP can significantly increase the vulcanization rate of styrene-butadiene rubber (SBR), and its resistance to thermal oxidative aging and extraction is significantly improved compared to the small-molecule antioxidant GM. Furthermore, our research group successfully prepared a chitosan-based macromolecular rubber antioxidant, COS-AO, by reacting the active hydroxyl and amino groups on low-molecular-weight chitosan oligosaccharides (COS) with a carboxyl-containing phenolic antioxidant (AO). COS-AO not only promotes rubber vulcanization but also significantly improves the rubber material's resistance to thermal oxidative aging (Patent Authorization Announcement No.: CN 112961263B). Therefore, by utilizing the two active groups, hydroxyl and amino, contained in the chitosan molecular structure to chemically bond functional small-molecule compounds to the chitosan backbone, it is possible to design and synthesize chitosan-based carriers for application in rubber materials. Summary of the Invention

[0006] In order to overcome the significant deficiencies of traditional small molecule rubber antioxidants, the primary purpose of the present invention is to provide a method for preparing an alkenyl chitosan-based multifunctional macromolecular rubber antioxidant.

[0007] The chitosan-based multifunctional macromolecular antioxidant provided by the present invention is prepared by first using acid and amino salt to protect the amino group, utilizing the active hydroxyl group on the chitosan to react with unsaturated fatty acids or unsaturated fatty acid halides, introducing a hydrocarbon chain with an unsaturated double bond into the chitosan structure, and then utilizing the active amino group on the deprotected chitosan to react with a small molecule antioxidant containing a carboxyl group, and further introducing a small molecule antioxidant into the chitosan structure. The chitosan-based multifunctional macromolecular antioxidant provided by the present invention is green and non-toxic, resistant to migration, and can not only significantly increase the rubber vulcanization rate, reduce the positive vulcanization time, and improve the comprehensive mechanical properties of the rubber, but also participate in the vulcanization cross-linking of the rubber through the introduced double bond, significantly improving the compatibility between the antioxidant and the rubber matrix, and at the same time having excellent long-term resistance to thermal oxidative aging and extraction resistance.

[0008] Another object of the present invention is to provide a chitosan-based multifunctional macromolecular rubber antioxidant prepared by the above method.

[0009] Another object of the present invention is to provide the use of the above-mentioned alkenyl-containing chitosan-based multifunctional macromolecular rubber antioxidant in the rubber field.

[0010] The purpose of the present invention is achieved through the following technical solutions:

[0011] A method for preparing an alkenyl-containing chitosan-based multifunctional macromolecular rubber antioxidant comprises the following steps:

[0012] (1) Chitosan (COS) is dissolved in an acidic solvent. After the acid forms a salt with the amino groups on the chitosan, unsaturated fatty acids and / or unsaturated fatty acyl halides (UA) are added, and the mixture is stirred at 0-80°C for 6-36 hours. The pH value of the reaction system is then adjusted to 8-10. The solid matter is filtered, purified, and dried to obtain a chitosan derivative containing a double-bonded hydrocarbon chain (COS-UA);

[0013] (2) After the chitosan derivative containing a double-bond hydrocarbon chain (COS-UA) is swollen in a solvent, a small molecule antioxidant containing a carboxyl group (B) is added, and the reaction is carried out at room temperature to 100°C for 12 to 72 hours under the action of a condensation agent and a catalyst. The reaction is then purified and dried to obtain a chitosan-based multifunctional macromolecular rubber antioxidant with alkenyl groups (COS-UA-B).

[0014] Preferably, the acidic solvent in step (1) is at least one of methanesulfonic acid, ethanesulfonic acid, and methanesulfonic acid / dimethyl sulfoxide (DMSO); the proton H + The molar ratio of the chain segments to the chitosan (COS) unit ring is ≥1; more preferably 1-22.

[0015] Preferably, the unsaturated fatty acid or unsaturated fatty acyl halide (UA) in step (1) has the following general structural formula:

[0016]

[0017] In the formula: X is selected from one of hydroxyl and halogen; R0 is an unsaturated aliphatic hydrocarbon chain.

[0018] More preferably, the unsaturated fatty acid in step (1) is at least one of butenoic acid, pentenoic acid, octenic acid, undecenoic acid, hexadecenoic acid (palmitoleic acid), octadecenoic acid (oleic acid), eicosenoic acid, linoleic acid, linolenic acid and arachidonic acid; further preferably, it is at least one of undecenoic acid, palmitoleic acid and linoleic acid.

[0019] More preferably, the unsaturated fatty acid halide in step (1) is at least one of crotonoyl halide, pentenoyl halide, octenoyl halide, undecenoyl halide, hexadecenoic acid halide (palmitoleic acid halide), octadecenoic acid halide (oleic acid halide), eicosenoic acid halide, linoleic acid halide, linolenic acid halide and arachidonic acid halide, wherein the halogen is at least one of chlorine, bromine and iodine; further preferably, the unsaturated fatty acid halide is undecenoyl chloride.

[0020] Preferably, in step (1), the molar ratio of the unsaturated fatty acid and / or unsaturated fatty acid halide (UA) to the chitosan (COS) unit ring is 0.5 to 3:1.

[0021] Preferably, the pH value of the reaction system in step (1) is adjusted with an alkaline solution, and the alkaline solution is at least one of sodium hydroxide solution, potassium hydroxide solution, sodium carbonate solution, potassium carbonate solution, sodium bicarbonate solution, and potassium bicarbonate solution.

[0022] Preferably, the purification in step (1) refers to washing the solid product with water until it becomes neutral.

[0023] The chemical reaction formula of step (1) is as follows:

[0024]

[0025] Preferably, the solvent in step (2) is at least one of methanol, dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMAC); and the volume ratio of the chitosan derivative containing a double-bonded hydrocarbon chain (COS-UA) to the solvent is 1 g: 20 to 120 mL.

[0026] Preferably, the swelling temperature in step (2) is 50 to 120° C., and the swelling time is 12 to 96 hours.

[0027] Preferably, the carboxyl-containing small molecule antioxidant (B) in step (2) has the following general structural formula:

[0028]

[0029] In the formula, R1, R2, R3, and R4 are at least one of tert-butyl, hydroxy, methoxy, methyl, and hydrogen, and at least one of R1, R2, R3, and R4 is a hydroxyl group;

[0030] Where y is any number between 0 and 1.

[0031] More preferably, the carboxyl-containing small molecule antioxidant (B) in step (2) is At least one of .

[0032] Preferably, the molar ratio of the carboxyl-containing small molecule antioxidant (B) and the chitosan derivative (COS-UA) unit ring containing a double-bond hydrocarbon chain in step (2) is 1 to 5:1.

[0033] Preferably, the molar ratio of the condensing agent in step (2) to the small molecule antioxidant containing a carboxyl group (B) is 1 to 3:1; the condensing agent is at least one of dicyclohexylcarbodiimide (DCC), diisopropylcarbodiimide (DIC), and 1-ethyl-(3-dimethylaminopropyl)carbodiimide (EDC); the molar ratio of the catalyst to the small molecule antioxidant containing a carboxyl group (B) is 0.05 to 1:1; the catalyst is at least one of N-hydroxysuccinimide (NHS), 4-dimethylaminopyridine (DMAP), and pyridine.

[0034] Preferably, the purification method in step (2) is: filtering the reaction product mixture to obtain solid matter and washing it.

[0035] The chemical reaction formula of step (2) above is as follows:

[0036]

[0037] When y=1, the carboxyl-containing small molecule antioxidant (B) is prepared by the following method:

[0038] A carboxyl-containing compound (A1) is dissolved in a solvent, a base is added to form a salt of the carboxyl group, and then a phenolic compound (A2) containing an aldehyde group is added. The reaction is carried out at room temperature to 80°C for 3 to 24 hours to form a Schiff base compound. The compound is reduced with a reducing agent, and the pH value of the system is adjusted to 3 to 5 with an acid. The compound is then filtered, purified, and dried to obtain a carboxyl-containing small molecule antioxidant (B). The specific synthesis reaction is shown below:

[0039]

[0040] Preferably, the amino group in the carboxyl-containing compound (A1) may be located at one of the 2nd, 3rd, and 4th positions of the benzene ring.

[0041] Preferably, the molar ratio of the carboxyl group-containing compound (A1) to the aldehyde group-containing phenolic compound (A2) is 1 to 3:1.

[0042] Preferably, the solvent is at least one of methanol, ethanol, isopropanol, and N,N-dimethylformamide (DMF); and the ratio of the carboxyl-containing compound (A1) to the solvent is 1 g: 5 to 20 mL.

[0043] Preferably, the base is at least one of sodium hydroxide and potassium hydroxide; and the molar ratio of the base to the carboxyl-containing compound (A1) is 1 to 1.5:1.

[0044] Preferably, the reducing agent is at least one of sodium borohydride, sodium cyanoborohydride, and lithium aluminum tetrahydride; and the molar ratio of the reducing agent to the aldehyde-containing phenolic compound (A2) is 1 to 1.5:1.

[0045] Preferably, the reaction temperature of the reducing agent reduction is 0 to 10° C., and the time is 2 to 10 hours.

[0046] Preferably, the acid is at least one of a hydrochloric acid solution and an acetic acid solution; the concentration of the hydrochloric acid solution is 10 to 36.5%, and the concentration of the acetic acid solution is 50 to 100%.

[0047] Preferably, the purification method is: first washing the solid product with water until it is neutral, and then performing Soxhlet extraction.

[0048] A chitosan-based multifunctional macromolecular rubber antioxidant with alkenyl groups is prepared by the above method.

[0049] Preferably, the general structural formula of the alkenyl-containing chitosan-based multifunctional macromolecular rubber antioxidant is as follows:

[0050]

[0051] Wherein R0 is an unsaturated aliphatic hydrocarbon chain;

[0052] In the formula, R1, R2, R3, and R4 are at least one of tert-butyl, hydroxy, methoxy, methyl, and hydrogen, and at least one of R1, R2, R3, and R4 is a hydroxyl group;

[0053] Where y is any number between 0 and 1.

[0054] The application of the above-mentioned alkenyl chitosan-based multifunctional macromolecular rubber antioxidant in the rubber field.

[0055] Preferably, the application is: when the alkenyl chitosan-based multifunctional macromolecular rubber antioxidant is used to prepare rubber products or rubber composite materials, the mass ratio of the alkenyl chitosan-based multifunctional macromolecular rubber antioxidant to rubber is 3 to 15:100.

[0056] A rubber product comprises the following components, calculated by mass: 100 parts of rubber, 1 to 3 parts of stearic acid, 2 to 8 parts of zinc oxide, 20 to 40 parts of carbon black and / or white carbon black, 3 to 15 parts of the above-mentioned alkenyl-containing chitosan-based multifunctional macromolecular rubber antioxidant, 1 to 3 parts of an accelerator CBS, and 1 to 3 parts of sulfur.

[0057] Preferably, the selected rubber is at least one of silicone rubber, natural rubber, butadiene rubber, styrene-butadiene rubber, isoprene rubber, and ethylene-propylene rubber.

[0058] The method for preparing the above-mentioned rubber product comprises the following steps:

[0059] (1) After the rubber is plasticized on an open mill, stearic acid, zinc oxide, carbon black and / or white carbon black, and the above-mentioned alkenyl chitosan-based multifunctional macromolecular rubber antioxidant are added in sequence, and after mixing evenly, accelerator CBS and sulfur are added and mixed evenly to obtain a mixed rubber.

[0060] (2) The rubber mixture obtained in step (1) is left to stand for a certain period of time and then subjected to sheeting and vulcanization to obtain the rubber product.

[0061] Preferably, the parking time in step (2) is 12 to 24 hours, the vulcanization temperature is 150 to 180°C, and the vulcanization time is the positive vulcanization time T at the corresponding vulcanization temperature. C90 .

[0062] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0063] (1) The molecular structure of the alkenyl chitosan-based multifunctional macromolecular rubber antioxidant provided by the present invention contains antioxidant groups such as amide and hindered phenol, which can play an intramolecular synergistic role in resisting thermal oxidative aging and has excellent thermal oxidative aging resistance for rubber materials.

[0064] (2) The chitosan structure in the alkenyl chitosan-based multifunctional macromolecular rubber antioxidant provided by the present invention has a synergistic effect with the small molecule antioxidant structure, which can significantly reduce the vulcanization time T C90 , promote rubber vulcanization and increase the vulcanization rate.

[0065] (3) The multifunctional macromolecular rubber antioxidant with olefinic chitosan provided by the present invention has a large molecular weight, and the unsaturated double bonds on the hydrocarbon chain in the structure can participate in the vulcanization and cross-linking of the rubber, significantly improving the compatibility between the antioxidant and the rubber matrix. It is not easy to volatilize, and has good resistance to migration and solvent extraction. It can exert a long-lasting anti-thermal oxidative aging effect on rubber materials and improve the comprehensive mechanical properties of rubber materials.

[0066] (4) The carrier of the alkenyl chitosan-based multifunctional macromolecular rubber antioxidant provided by the present invention is natural high-molecular chitosan, which is abundant in source, low in price, and green and environmentally friendly. The hydroxyl and amino groups in its structure have high reactivity and are easier to be chemically modified. Using chitosan as the raw material of the rubber antioxidant is not only conducive to fully broadening the application scope of chitosan and realizing the comprehensive utilization of biomass materials, but also meets the development requirements of "green chemistry". DETAILED DESCRIPTION

[0067] The present invention will be further described in detail below with reference to examples, but the embodiments of the present invention are not limited thereto.

[0068] In the examples of the present invention, if no specific conditions are specified, the experiments were carried out under conventional conditions or the conditions recommended by the manufacturer. All raw materials and reagents used without manufacturer's name are commercially available conventional products.

[0069] Example 1: Synthesis of alkenyl chitosan-based multifunctional macromolecular rubber antioxidant COS-UA-B-1

[0070] (1) In a 250 mL three-necked flask, 5 g (29.0 mmol molar number of unit ring) of chitosan (COS) and 70 mL of a mixed solvent of methanesulfonic acid / dimethyl sulfoxide (350.0 mmol H + ), stirring at room temperature to allow the amino groups in the chitosan structure to be completely salified and dissolved in the solvent; then, 2.9 g (14.5 mmol) of 10-undecenoyl chloride (UA) was added, and the reaction was stirred at 0°C for 36 hours. The pH of the reaction system was adjusted to 8 with a saturated sodium bicarbonate solution. The precipitated solid product was washed with water to neutrality, filtered, and purified, and then dried to constant weight to obtain a chitosan derivative containing a double-bond hydrocarbon chain (COS-UA-1).

[0071] (2) Add 5.0g of the product COS-UA-1 obtained in step (1) and 50mL of methanol to a 250mL three-necked flask, stir at 50°C for 96 hours to fully expand COS-UA-1; then add 4.9g (29.0mmol) of carboxyl-containing gallic acid small molecule antioxidant B-1, 18.0g (87.0mmol) of dicyclohexylcarbodiimide (DCC), 3.3g (29.0mmol) of N-hydroxysuccinimide (NHS) and 50mL of methanol, and react at room temperature for 72 hours. The reaction product mixture is filtered and washed, and then dried to constant weight to obtain alkenyl chitosan-based multifunctional macromolecular rubber antioxidant COS-UA-B-1.

[0072] The structural formula of B-1 is a special case of the general structural formula of the carboxyl-containing small molecule antioxidant (B), wherein y=0, R1 is a hydrogen atom, and R2, R3, and R4 are hydroxyl groups. The simplified structural formula of B-1 is as follows:

[0073]

[0074] Infrared spectrum characterization results of COS-UA-B-1: COS-UA-B-1 at 2930cm -1 and 2859cm -1 and 720cm -1 The characteristic peak at 3077cm is attributed to the vibration peak of the methylene group on the unsaturated fatty hydrocarbon chain. -1 The characteristic peak at 906 cm is attributed to the stretching vibration peak of the carbon-hydrogen single bond on the carbon-carbon double bond in the unsaturated aliphatic hydrocarbon chain. -1 The characteristic peak at 1739cm is attributed to the bending vibration peak of the carbon-hydrogen single bond on the carbon-carbon double bond in the unsaturated aliphatic hydrocarbon chain. -1 The characteristic peak at 1657 cm is attributed to the ester carbonyl vibration peak. -1 and 1566cm -1 The characteristic peaks at 1440 cm-1 are attributed to the vibration peaks of amide I and amide II generated by the reaction between the amino groups on the chitosan skeleton and the carboxyl groups in gallic acid. -1 The characteristic peak at is attributed to the skeleton vibration peak of benzene ring. The infrared analysis results show that the structure of the prepared alkenyl chitosan-based multifunctional macromolecular rubber antioxidant COS-UA-B-1 is consistent with the structure described above.

[0075] Elemental analysis results of COS-UA-1 and COS-UA-B-1: The substitution degrees of COS-UA-1 and COS-UA-B-1 were 0.42 and 0.51, respectively. Elemental analysis results showed that the substitution degrees of UA and small molecule antioxidant B on chitosan were significantly higher than those in Comparative Example 1.

[0076] Example 2: Synthesis of alkenyl chitosan-based multifunctional macromolecular rubber antioxidant COS-UA-B-2

[0077] (1) Add 5 g (unit ring mole number 29.0 mmol) chitosan (COS) and 50 mL (613.0 mmol H + ) ethanesulfonic acid, stirring at room temperature to allow the amino groups in the chitosan structure to be completely salified and dissolved in the solvent; then adding 9.2 g (36.3 mmol) of palmitic acid (UA), stirring and reacting at 40°C for 20 hours, adjusting the pH of the reaction system to 9 with 1 mol / L sodium hydroxide solution, washing the precipitated solid product with water to neutrality, and after purification through post-treatment such as filtration and washing, drying to constant weight to obtain a chitosan derivative COS-UA-2 containing a double-bond hydrocarbon chain.

[0078] (2) Add 5.0 g of the product COS-UA-1 obtained in step (1) and 100 mL of dimethyl sulfoxide to a 250 mL three-necked flask, and stir at 85° C. for 54 hours to allow COS-UA-2 to fully expand; then add 30.9 g (87.0 mmol) of a carboxyl-containing small molecule antioxidant B-2, 36.0 g (174.0 mmol) of dicyclohexylcarbodiimide (DCC), 5.0 g (43.5 mmol) of N-hydroxysuccinimide (NHS) and 300 ml of methanol, and react at 65° C. for 42 hours. The resulting reaction product is purified by post-treatment such as filtration and washing, and then dried to constant weight to obtain COS-UA-B-2, a multifunctional macromolecular rubber antioxidant based on alkenyl chitosan.

[0079] The preparation process of the carboxyl-containing small molecule antioxidant B-2 is as follows:

[0080] To a 500mL three-necked flask, 18.8g (80mmol) of 3,5-di-tert-butyl salicylaldehyde and 100mL of ethanol were added. To a 250mL beaker, 11.0g (80mmol) of p-aminobenzoic acid and 100mL of ethanol were added. After stirring to dissolve, 50mL of potassium hydroxide (4.5gKOH, 80mmol) solution was added dropwise to the 3,5-di-tert-butyl salicylaldehyde solution. The mixture was stirred and reacted at 80°C for 3 hours. After the reaction, the mixture was cooled, and 3.0g (80mmol) of sodium borohydride (a reducing agent) was added at 0°C. The reaction was stirred for 2 hours, and the pH was adjusted to 3 with 36.5% hydrochloric acid solution. The precipitated solid product was filtered, washed with water until neutral, purified by Soxhlet extraction, and dried to constant weight to obtain a carboxyl-containing small molecule antioxidant B-2.

[0081] The structural formula of B-2 is a special case of the general structural formula of the carboxyl-containing small molecule antioxidant (B), wherein y=1, R1 is a hydroxyl group, R2 and R4 are tert-butyl groups, and R3 is a hydrogen atom. The simplified structural formula of B-2 is as follows:

[0082]

[0083] Infrared spectrum characterization results of COS-UA-B-2: COS-UA-B-2 at 2933cm -1 and 2857cm -1 The characteristic peak at 3078 cm is attributed to the stretching vibration peak of the methylene group on the unsaturated aliphatic hydrocarbon chain. -1 The characteristic peak at 906 cm is attributed to the stretching vibration peak of the carbon-hydrogen single bond on the carbon-carbon double bond in the unsaturated aliphatic hydrocarbon chain. -1 The characteristic peak at 1744 cm is attributed to the bending vibration peak of the carbon-hydrogen single bond on the carbon-carbon double bond in the unsaturated aliphatic hydrocarbon chain. -1 The characteristic peak at 1660 cm is attributed to the ester carbonyl vibration peak. -1 and 1545cm -1 The characteristic peaks at 1465 cm-1 are respectively attributed to the vibration peaks of amide I and amide II generated by the reaction between the amino groups on the chitosan skeleton and the carboxyl groups in the antioxidant B-2. -1 The characteristic peak at is attributed to the skeleton vibration of the benzene ring. The infrared analysis results show that the structure of the prepared alkenyl chitosan-based multifunctional macromolecular rubber antioxidant COS-UA-B-2 is consistent with the structure described above.

[0084] Elemental analysis results of COS-UA-2 and COS-UA-B-2: The substitution degrees of COS-UA-2 and COS-UA-B-2 were 0.58 and 0.62, respectively. Elemental analysis results showed that the substitution degrees of UA and small molecule antioxidant B on chitosan were significantly higher than those in Comparative Example 1.

[0085] Example 3: Synthesis of alkenyl chitosan-based multifunctional macromolecular rubber antioxidant COS-UA-B-3

[0086] (1) In a 250 mL three-necked flask, 5 g (29.0 mmol molar number of unit ring) of chitosan (COS) and 70 mL of a mixed solvent of methanesulfonic acid / dimethyl sulfoxide (38.0 mmol H + ), stirring at room temperature to allow the amino groups in the chitosan structure to be completely salified and dissolved in the solvent; then adding 16.3 g (58 mmol) of linoleic acid (UA), stirring and reacting at 80°C for 6 hours, after which the reaction is completed, pouring the mixture into ice water, adjusting the pH to 10 with 5 mol / L potassium hydroxide solution, washing the precipitated solid product with water until neutral, filtering, and drying to constant weight to obtain a chitosan derivative COS-UA-3 containing a double-bond hydrocarbon chain.

[0087] (2) Add 5.0 g of the product COS-UA-3 obtained in step (1) and 100 mL of N,N-dimethylformamide to a 250 ml three-necked flask, and stir at 120° C. for 12 hours to fully expand COS-UA-3; then add 51.6 g (145 mmol) of a carboxyl-containing small molecule antioxidant B-3, 18.3 g (145 mmol) of diisopropylcarbodiimide (DIC), 0.6 g (7.3 mmol) of pyridine, and 500 ml of N,N-dimethylformamide, and react at 100° C. for 12 hours. The resulting reaction product is purified by post-treatment such as filtration and washing, and then dried to obtain a chitosan-based multifunctional macromolecular rubber antioxidant COS-UA-B-3 with alkenyl groups.

[0088] The preparation process of the carboxyl small molecule antioxidant B-3 is as follows:

[0089] To a 500mL three-necked flask, 12.2g (80mmol) of 3-methyl-2,4-dihydroxybenzaldehyde and 100ml of N,N-dimethylformamide were added. To a 250mL beaker, 32.9g (240mmol) of 3-aminobenzoic acid and 250ml of N,N-dimethylformamide were added and stirred to dissolve. 100ml of sodium hydroxide solution (14.4g NaOH, 360mol) was added dropwise to the 3-methyl-2,4-dihydroxybenzaldehyde solution and stirred at room temperature for 24 hours. After the reaction, the mixture was cooled and 7.5g (120mmol) of sodium cyanoborohydride (a reducing agent) was added at 5°C. The reaction was stirred for 3 hours. Finally, the pH was adjusted to 5 with 80% acetic acid solution. The precipitated solid product was filtered, washed with water until neutral, purified by Soxhlet extraction, and dried to constant weight to obtain a carboxyl-containing small molecule antioxidant B-3.

[0090] The structural formula of B-3 is a special case of the general structural formula of the carboxyl-containing small molecule antioxidant (B), wherein y=1, R1 and R3 are hydroxyl groups, R2 is a methyl group, and R4 is a hydrogen atom. The simplified structural formula of B-3 is as follows:

[0091]

[0092] Infrared spectrum characterization results of COS-UA-B-3: COS-UA-B-3 at 2928cm -1 and 2856cm -1 The characteristic peak at 3077cm is attributed to the stretching vibration peak of the methylene group on the unsaturated aliphatic hydrocarbon chain. -1 The characteristic peak at 906 cm is attributed to the stretching vibration peak of the carbon-hydrogen single bond on the carbon-carbon double bond in the unsaturated aliphatic hydrocarbon chain. -1 The characteristic peak at 1744 cm is attributed to the bending vibration peak of the carbon-hydrogen single bond on the carbon-carbon double bond in the unsaturated aliphatic hydrocarbon chain. -1The characteristic peak at 1657 cm is attributed to the ester carbonyl vibration peak. -1 and 1560cm -1 The characteristic peaks at 1445 cm-1 are respectively attributed to the vibration peaks of amide I and amide II generated by the reaction between the amino groups on the chitosan skeleton and the carboxyl groups in the antioxidant B-3. -1 The characteristic peak at is attributed to the skeleton vibration of the benzene ring. The infrared analysis results show that the structure of the prepared alkenyl chitosan-based multifunctional macromolecular rubber antioxidant COS-UA-B-3 is consistent with the structure described above.

[0093] Elemental analysis results of COS-UA-3 and COS-UA-B-3: The substitution degrees of COS-UA-3 and COS-UA-B-3 were 0.86 and 0.70, respectively. Elemental analysis results showed that the substitution degrees of UA and small molecule antioxidant B on chitosan were significantly higher than those in Comparative Example 1.

[0094] Comparative Example 1: Synthesis of Chitosan-based Rubber Antioxidant COS-UA-B-4

[0095] (1) In a 250 mL three-necked flask, 5 g (29.0 mmol molar number of unit rings) of chitosan (COS) and 70 mL of dimethyl sulfoxide solvent were added, followed by the addition of 16.3 g (58 mmol) of linoleic acid (UA). The mixture was stirred at 80°C for 6 hours. After the reaction, the mixture was poured into ice water and adjusted to pH = 10 with 5 mol / L potassium hydroxide solution. The solid product was washed with water until neutral, filtered, and dried to constant weight to obtain a chitosan derivative containing a double-bond hydrocarbon chain, COS-UA-4.

[0096] (2) 5.0 g of the product COS-UA-4 obtained in step (1) and 100 mL of N,N-dimethylformamide were added to a 250 mL three-necked flask and stirred at 120° C. for 12 hours to allow COS-UA-4 to fully expand. 51.6 g (145 mmol) of a carboxyl-containing small molecule antioxidant B-3, 18.3 g (145 mmol) of diisopropylcarbodiimide (DIC), 0.6 g (7.3 mmol) of pyridine, and 500 mL of N,N-dimethylformamide were then added and reacted at 100° C. for 12 hours. The resulting reaction product was purified by post-treatment such as filtration and washing, and then dried to obtain a chitosan-based rubber antioxidant COS-UA-B-4.

[0097] Infrared spectrum characterization results of COS-UA-B-4: COS-UA-B-4 at 2930cm -1 and 2857cm -1 The characteristic peak at 3079cm is attributed to the stretching vibration peak of the methylene group on the unsaturated aliphatic hydrocarbon chain. -1The characteristic peak at 909cm is attributed to the stretching vibration peak of the carbon-hydrogen single bond on the carbon-carbon double bond in the unsaturated aliphatic hydrocarbon chain. -1 The characteristic peak at 1744 cm is attributed to the bending vibration peak of the carbon-hydrogen single bond on the carbon-carbon double bond in the unsaturated aliphatic hydrocarbon chain. -1 The characteristic peak at 1655 cm is attributed to the ester carbonyl vibration peak. -1 and 1560cm -1 The characteristic peaks at 1445 cm are respectively attributed to the vibration peaks of amide I and amide II generated by the reaction of amino groups on the chitosan skeleton with the carboxyl groups in antioxidant B-3 or linoleic acid. -1 The characteristic peak at is attributed to the skeleton vibration of the benzene ring. The infrared analysis results show that the structure of the prepared alkenyl chitosan-based multifunctional macromolecular rubber antioxidant COS-UA-B-4 is consistent with the structure described above.

[0098] Elemental analysis results of COS-UA-4 and COS-UA-B-4: The degrees of substitution of COS-UA-4 and COS-UA-B-4 were 0.11 and 0.12, respectively. Elemental analysis results showed that the degrees of substitution of UA and small molecule antioxidant B on chitosan were significantly lower than those in Examples 1, 2, and 3.

[0099] Example 4: Application of alkenyl-containing chitosan-based multifunctional macromolecular rubber antioxidant COS-UA-B-1 in styrene-butadiene rubber.

[0100] (1) After 100 parts of styrene-butadiene rubber were plasticized and thinned for 6 times on an open mill, 2 parts of stearic acid, 5 parts of zinc oxide, 30 parts of white carbon black, and 3.6 parts of alkenyl chitosan-based multifunctional macromolecular rubber antioxidant COS-UA-B-1 were added in sequence and mixed evenly. Then, 2 parts of accelerator CBS and 2 parts of sulfur were added and mixed evenly to obtain a rubber compound containing alkenyl chitosan-based multifunctional macromolecular rubber antioxidant.

[0101] (2) The rubber mix obtained in step (1) was placed on a flat vulcanizing machine for 24 hours and then tableted. C90 Vulcanization: The temperature of the press plate vulcanization is 160°C. After the vulcanized samples are placed at room temperature for 24 hours, mechanical properties tests, thermal oxidation aging resistance tests, and extraction resistance tests are performed.

[0102] The curing characteristic parameters of the styrene-butadiene rubber compound of this embodiment are shown in Table 1, the mechanical property parameters are shown in Table 2, and the thermal oxidative aging resistance and extraction resistance are shown in Table 3.

[0103] As can be seen from Table 1, ① the curing time T of the styrene-butadiene rubber compound of the present embodiment is C90 is 14.83min, and the vulcanization rate index CRI is 10.57; compared with comparative example 2, the positive vulcanization time T of this embodiment is C90The curing rate index CRI is significantly increased, indicating that the addition of COS-UA-B-1 has a significant promoting effect on the curing of styrene-butadiene rubber; ② The minimum torque (M L )、Maximum torque (M H ) and △M are greater than those of the styrene-butadiene rubber compound of Comparative Example 2, indicating that the addition of COS-UA-B-1 improves the degree of crosslinking of the styrene-butadiene rubber compound.

[0104] As can be seen from Table 2, the styrene butadiene vulcanizate of this embodiment is greater than the styrene butadiene vulcanizate of Comparative Example 2 in tensile strength, 100% modulus of tensile stress, 300% modulus of tensile stress, and elongation at break, indicating that the addition of COS-UA-B-1 improves the mechanical properties of the styrene butadiene vulcanizate.

[0105] As can be seen from Table 3, ① the styrene butadiene vulcanizate of this embodiment has a greater tensile aging coefficient (k) than Comparative Examples 2, 3, and 4, indicating that the styrene butadiene vulcanizate with the addition of COS-UA-B-1 has better resistance to thermal oxidative aging. ② After 72 hours of methanol extraction followed by 48 hours of accelerated thermal oxidative aging at 100°C, the tensile aging coefficient (k) of this embodiment decreased from 0.79 to 0.62, and the aging coefficient retention rate reached 78.5%. This indicates that COS-UA-B-1 has excellent extraction resistance, is superior to commercial antioxidants 264 and MB, and can provide long-lasting resistance to thermal oxidative aging for styrene butadiene vulcanizate.

[0106] Example 5: Application of alkenyl-containing chitosan-based multifunctional macromolecular rubber antioxidant COS-UA-B-2 in SBR rubber.

[0107] (1) After 100 parts of styrene-butadiene rubber were plasticized and thinned for 6 times on an open mill, 2 parts of stearic acid, 5 parts of zinc oxide, 30 parts of white carbon black, and 4.7 parts of alkenyl chitosan-based multifunctional macromolecular rubber antioxidant COS-UA-B-2 were added in sequence and mixed evenly. Then, 2 parts of accelerator CBS and 2 parts of sulfur were added and mixed evenly to obtain a rubber compound containing alkenyl chitosan-based multifunctional macromolecular rubber antioxidant.

[0108] (2) The rubber mix obtained in step (1) was placed on a flat vulcanizing machine for 24 hours and then tableted. C90 Vulcanization: The temperature of the press plate vulcanization is 160°C. After the vulcanized samples are placed at room temperature for 24 hours, mechanical properties tests, thermal oxidation aging resistance tests, and extraction resistance tests are performed.

[0109] The curing characteristic parameters of the styrene-butadiene rubber compound of this embodiment are shown in Table 1, the mechanical property parameters are shown in Table 2, and the thermal oxidative aging resistance and extraction resistance are shown in Table 3.

[0110] As can be seen from Table 1, ① the curing time T of the styrene-butadiene rubber compound of the present embodiment is C90is 14.06min, and the vulcanization rate index CRI is 11.06; compared with comparative example 2, the positive vulcanization time T of this embodiment is C90 The curing rate index CRI is significantly increased, indicating that the addition of COS-UA-B-2 has a significant promoting effect on the curing of styrene-butadiene rubber; ② The minimum torque (M L )、Maximum torque (M H ) and △M are greater than those of the styrene-butadiene rubber compound of Comparative Example 2, indicating that the addition of COS-UA-B-2 improves the degree of crosslinking of the styrene-butadiene rubber compound.

[0111] As can be seen from Table 2, the tensile strength, 100% modulus of tensile stress, 300% modulus of tensile stress, and elongation at break of the styrene butadiene vulcanizate of this embodiment are all greater than those of the styrene butadiene vulcanizate of Comparative Example 2, indicating that the addition of COS-UA-B-2 improves the mechanical properties of the styrene butadiene vulcanizate.

[0112] As shown in Table 3, ① the styrene butadiene rubber vulcanizate of this embodiment has a greater tensile aging coefficient (k) than Comparative Examples 2, 3, and 4, indicating that the styrene butadiene rubber vulcanizate with the addition of COS-UA-B-2 has better resistance to thermal oxidative aging. ② After 72 hours of methanol extraction and then 48 hours of accelerated thermal oxidative aging at 100°C, the tensile aging coefficient (k) of this embodiment decreased from 0.74 to 0.57, with a k value retention rate of 77.0%. This indicates that COS-UA-B-2 has good extraction resistance, is superior to commercial antioxidants 264 and MB, and can provide a lasting thermal oxidative aging effect on styrene butadiene rubber.

[0113] Example 6: Application of alkenyl-containing chitosan-based multifunctional macromolecular rubber antioxidant COS-UA-B-3 in SBR rubber.

[0114] (1) After 100 parts of SBR rubber were plasticized and thinned for 6 times on an open mill, 2 parts of stearic acid, 5 parts of zinc oxide, 30 parts of white carbon black, and 10 parts of alkenyl chitosan-based multifunctional macromolecular rubber antioxidant CS-UA-B-3 were added in sequence and mixed evenly. Then, 2 parts of accelerator CBS and 2 parts of sulfur were added and mixed evenly to obtain a rubber compound containing alkenyl chitosan-based multifunctional macromolecular rubber antioxidant.

[0115] (2) The rubber mix obtained in step (1) was placed on a flat vulcanizing machine for 24 hours and then tableted. C90 Vulcanization: The temperature of the press plate vulcanization is 160°C. After the vulcanized samples are placed at room temperature for 24 hours, mechanical properties tests, thermal oxidation aging resistance tests, and extraction resistance tests are performed.

[0116] The curing characteristic parameters of the styrene-butadiene rubber compound of this embodiment are shown in Table 1, the mechanical property parameters are shown in Table 2, and the thermal oxidative aging resistance and extraction resistance are shown in Table 3.

[0117] As can be seen from Table 1, ① the curing time T of the styrene-butadiene rubber compound of the present embodiment is C90 The curing time T is 14.27min and the curing rate index CRI is 10.17. Compared with the comparative example 2, the curing time T is C90 The curing rate index CRI is significantly increased, indicating that the addition of COS-UA-B-3 has a significant promoting effect on the curing of styrene-butadiene rubber; ② The minimum torque (M L )、Maximum torque (M H ) and △M are greater than those of the styrene-butadiene rubber compound of Comparative Example 2, indicating that the addition of COS-UA-B-3 improves the degree of crosslinking of the styrene-butadiene rubber compound.

[0118] As can be seen from Table 2, ① the tensile strength, 100% modulus, 300% modulus, and elongation at break of the styrene-butadiene vulcanizate of this embodiment are all greater than those of the styrene-butadiene vulcanizate of Comparative Example 2, indicating that the addition of COS-UA-B-3 improves the mechanical properties of the styrene-butadiene rubber compound.

[0119] As can be seen from Table 3, ① the styrene butadiene vulcanizate of this embodiment has a greater tensile aging coefficient (k) than Comparative Examples 2, 3, and 4, indicating that the styrene butadiene vulcanizate with the addition of COS-UA-B-3 has better resistance to thermal oxidative aging. ② After 72 hours of methanol extraction and then 48 hours of accelerated thermal oxidative aging at 100°C, the tensile aging coefficient (k) of this embodiment decreased from 0.77 to 0.59, with a k value retention rate of 76.6%. This indicates that COS-UA-B-3 has good extraction resistance, is superior to commercial antioxidants 264 and MB, and can provide a lasting thermal oxidative aging effect on styrene butadiene vulcanizate.

[0120] Comparative Example 2: Styrene-butadiene rubber without adding rubber antioxidant

[0121] In order to illustrate the vulcanization accelerating effect, mechanical reinforcing effect and thermal oxidative aging resistance of the alkenyl chitosan-based multifunctional macromolecular rubber antioxidant of the present invention, styrene-butadiene rubber without the rubber antioxidant was used as a comparative example.

[0122] (1) After 100 parts of SBR rubber were plasticized and thinned on an open mill for 6 times, 2 parts of stearic acid, 5 parts of zinc oxide, and 30 parts of white carbon black were added in sequence and mixed evenly. Then, 2 parts of accelerator CBS and 2 parts of sulfur were added and mixed evenly to obtain an SBR compound without rubber antioxidant.

[0123] (2) The rubber mix obtained in step (1) was placed on a flat vulcanizing machine for 24 hours and then tableted. C90 Vulcanization: The temperature of the press plate vulcanization is 160°C. After the vulcanized samples are placed at room temperature for 24 hours, mechanical properties tests, thermal oxidation aging resistance tests, and extraction resistance tests are performed.

[0124] The curing characteristic parameters of the styrene-butadiene rubber compound of this comparative example are shown in Table 1, the mechanical property parameters are shown in Table 2, and the thermal oxidative aging resistance and extraction resistance are shown in Table 3.

[0125] As can be seen from Table 1, ① the curing time T of the styrene-butadiene rubber compound of this comparative example C90 The curing time T is 18.92min, and the curing rate index CRI is 8.62. Compared with Example 4, Example 5 and Example 6, the curing time T is 18.92min, and the curing rate index CRI is 8.62. C90 The curing rate index CRI is obviously smaller, indicating that the curing rate of the styrene-butadiene rubber compound of this comparative example is obviously slower than that of Example 4, Example 5 and Example 6. ② The minimum torque (M L )、Maximum torque (M H ) and △M are smaller than those of the styrene-butadiene rubber mixtures of Examples 4, 5 and 6, indicating that the degree of crosslinking of the styrene-butadiene rubber mixture of this comparative example is lower than those of Examples 4, 5 and 6.

[0126] As can be seen from Table 2, the tensile strength, 100% modulus of tensile stress, 300% modulus of tensile stress and elongation at break of the styrene-butadiene vulcanizate of this comparative example are all less than those of the styrene-butadiene vulcanizate of Examples 4, 5 and 6, indicating that the mechanical properties of this comparative example are worse than those of Examples 4, 5 and 6.

[0127] As can be seen from Table 3, the tensile product aging coefficient (k) of the styrene butadiene vulcanizate in this comparative example is only 0.52, indicating that the styrene butadiene vulcanizate without the addition of a rubber antioxidant has poor resistance to thermal oxidative aging. After 72 hours of methanol extraction and then 48 hours of accelerated thermal oxidative aging at 100°C, the tensile product aging coefficient (k) of the styrene butadiene vulcanizate in this comparative example dropped to 0.19, indicating that its resistance to thermal oxidative aging has further weakened.

[0128] Comparative Example 3: Styrene-butadiene rubber with commercial antioxidant 264 added

[0129] In order to illustrate the advantages of the alkenyl chitosan-based multifunctional macromolecular rubber antioxidant of the present invention, styrene-butadiene rubber to which the common industrial rubber antioxidant 264 is added is used as a comparative example.

[0130] (1) After 100 parts of SBR rubber were plasticized and thinned on an open mill for 6 times, 2 parts of stearic acid, 5 parts of zinc oxide, 30 parts of white carbon black, and 2 parts of antioxidant 264 were added in sequence and mixed evenly. Then, 2 parts of accelerator CBS and 2 parts of sulfur were added and mixed evenly to obtain a rubber compound containing rubber antioxidant 264.

[0131] (2) The rubber mix obtained in step (1) was placed on a flat vulcanizing machine for 24 hours and then tableted. C90Vulcanization: The temperature of the press plate vulcanization is 160°C. After the vulcanized samples are placed at room temperature for 24 hours, mechanical properties tests, thermal oxidation aging resistance tests, and extraction resistance tests are performed.

[0132] The thermal oxidative aging resistance of the styrene-butadiene vulcanizate of this comparative example is shown in Table 3.

[0133] As can be seen from Table 3, the tensile product aging coefficient (k) of the styrene butadiene vulcanizate of this comparative example is 0.64. Compared with Comparative Example 1, the tensile product aging coefficient (k) is significantly increased, indicating that the addition of rubber antioxidant 264 can improve the thermal oxidative aging resistance of the styrene butadiene vulcanizate. However, compared with Examples 4, 5 and 6, the tensile product aging coefficient (k) of the styrene butadiene vulcanizate of this comparative example is significantly smaller, indicating that the thermal oxidative aging resistance of the styrene butadiene vulcanizate of this comparative example is not as good as those of Examples 4, 5 and 6.

[0134] Comparative Example 4: Styrene-butadiene rubber with commercial antioxidant MB added

[0135] In order to illustrate the anti-thermal oxidative aging performance and extraction resistance of the alkenyl chitosan-based multifunctional macromolecular rubber antioxidant of the present invention, styrene-butadiene rubber to which the common industrial rubber antioxidant MB is added is used as a comparative example.

[0136] (1) After 100 parts of styrene-butadiene rubber were plasticized and thinned for 6 times on an open mill, 2 parts of stearic acid, 5 parts of zinc oxide, 30 parts of white carbon black, and 2 parts of antioxidant MB were added in sequence and mixed evenly. Then, 2 parts of accelerator CBS and 2 parts of sulfur were added and mixed evenly to obtain a rubber compound containing antioxidant MB.

[0137] (2) The rubber mix obtained in step (1) was placed on a flat vulcanizing machine for 24 hours and then tableted. C90 Vulcanization: The temperature of the press plate vulcanization is 160°C. After the vulcanized samples are placed at room temperature for 24 hours, mechanical properties tests, thermal oxidation aging resistance tests, and extraction resistance tests are performed.

[0138] The thermal oxidative aging resistance and extraction resistance of the styrene-butadiene vulcanizate of this comparative example are shown in Table 3.

[0139] As can be seen from Table 3, the tensile aging coefficient (k) of the styrene butadiene vulcanizate of this comparative example is 0.71, which is significantly higher than that of Comparative Example 1, indicating that the styrene butadiene vulcanizate with the addition of rubber antioxidant MB exhibits better resistance to thermal oxidative aging. However, the tensile aging coefficient (k) is lower than that of the styrene butadiene vulcanizates of Examples 4, 5, and 6, indicating that the thermal oxidative aging resistance of the styrene butadiene vulcanizate of this comparative example is not as good as that of Examples 4, 5, and 6. After 72 hours of methanol extraction and then 48 hours of accelerated thermal oxidative aging at 100°C, the tensile aging coefficient (k) of the styrene butadiene vulcanizate of this comparative example decreased from 0.71 to 0.36, and the k value retention rate was 50.7%, which is significantly lower than the tensile aging coefficient (k) retention rates of Examples 4, 5, and 6, indicating that the extraction resistance of antioxidant MB is not as good as that of the alkenyl chitosan-based multifunctional macromolecular rubber antioxidant COS-UA-B.

[0140] Comparative Example 5: Styrene-butadiene rubber with COS-UA-B-4 added

[0141] In order to illustrate the necessity of first using acid to salt the amino groups on chitosan to protect the amino groups when synthesizing the alkenyl chitosan-based multifunctional macromolecular rubber antioxidant described in the present invention, a styrene-butadiene rubber to which COS-UA-B-4 synthesized under conditions in which the amino groups on chitosan are not protected is added is used as a comparative example.

[0142] (1) After 100 parts of SBR rubber were plasticized and thinned for 6 times on an open mill, 2 parts of stearic acid, 5 parts of zinc oxide, 30 parts of white carbon black, and 10 parts of chitosan-based multifunctional macromolecular rubber antioxidant CS-UA-B-4 were added in sequence and mixed evenly. Then, 2 parts of accelerator CBS and 2 parts of sulfur were added and mixed evenly to obtain a compound rubber containing chitosan-based multifunctional macromolecular rubber antioxidant.

[0143] (2) The rubber mix obtained in step (1) was placed on a flat vulcanizing machine for 24 hours and then tableted. C90 Vulcanization: The temperature of the press plate vulcanization is 160°C. After the vulcanized samples are placed at room temperature for 24 hours, mechanical properties tests, thermal oxidation aging resistance tests, and extraction resistance tests are performed.

[0144] The curing characteristic parameters of the styrene-butadiene rubber compound of this comparative example are shown in Table 1, the mechanical property parameters are shown in Table 2, and the thermal oxidative aging resistance and extraction resistance are shown in Table 3.

[0145] As can be seen from Table 1, ① the curing time T of the styrene-butadiene rubber compound of this comparative example C90 The curing time T is 16.68min and the curing rate index CRI is 9.44. Compared with Example 6, the curing time T is C90The curing rate index CRI is obviously smaller, indicating that the curing rate of the styrene-butadiene rubber compound of this comparative example is obviously slower than that of Example 6. ② The minimum torque (M L )、Maximum torque (M H ) and △M are both smaller than those of the styrene-butadiene rubber compound of Example 6, indicating that the degree of crosslinking of the styrene-butadiene rubber compound of this comparative example is lower than that of Example 6.

[0146] As can be seen from Table 2, the tensile strength, 100% modulus of elongation, 300% modulus of elongation and elongation at break of the styrene butadiene vulcanizate of this comparative example are all lower than those of the styrene butadiene vulcanizate of Example 6, indicating that the mechanical properties of this comparative example are worse than those of Example 6.

[0147] As can be seen from Table 3, the tensile aging coefficient (k) of the styrene butadiene vulcanizate in this comparative example is only 0.61. Compared with Example 6, the tensile aging coefficient (k) is significantly reduced, indicating that the thermal oxidative aging resistance of the styrene butadiene vulcanizate in this comparative example is not as good as that of Example 6.

[0148] Characterization methods

[0149] 1. Elemental analysis of COS-UA and COS-UA-B: The C, H, and N contents of COS, COS-UA, and COS-UA-B were measured using an elemental analyzer. The degree of substitution (DS) was calculated according to formula (1).

[0150]

[0151] Where: represent the atomic number ratios of C and N in the samples before and after grafting, respectively; X and Y represent the number of carbon atoms and nitrogen atoms in the grafted small molecule structure, respectively.

[0152] 2. Tensile strength and elongation at break test of styrene-butadiene rubber samples: carried out in accordance with GB / T 528-2009.

[0153] 3. Thermal oxygen aging resistance test of styrene-butadiene rubber samples: According to GB / T 3512-2001, the aging temperature is 100°C and the aging duration is 48h.

[0154] The aging coefficient (k) is used as an evaluation index for aging resistance. The tensile product f = tensile strength × elongation at break. The aging coefficient (k) is determined by the tensile product before and after aging. The aging coefficient (k) is calculated using formula (2). The larger the k value, the stronger the aging resistance.

[0155]

[0156] Where: k-aging coefficient; f a - tensile strength of the sample after aging; fb -Tensile product of unaged specimens.

[0157] 4. Test of solvent extraction resistance of antioxidant: extract and soak in methanol for 72 hours, then perform thermal oxygen accelerated aging (100℃×48h). The tensile aging coefficient retention rate k before and after extraction is used to calculate the value of the solvent extraction resistance of antioxidant. r Characterizes the quality of extraction resistance, k r The larger the value, the better the extraction resistance. r Calculate according to formula (3):

[0158]

[0159] Where: k r -Aging coefficient retention rate;

[0160] k-Aging coefficient after methanol extraction for 72 hours and then accelerated aging at 100℃ for 48 hours;

[0161] k0-Aging coefficient after direct accelerated aging at 100℃ for 48h without extraction treatment.

[0162] Table 1 Vulcanization characteristic parameters of styrene-butadiene rubber compound

[0163]

[0164] Table 2 Mechanical properties of styrene-butadiene rubber vulcanizate

[0165]

[0166] Table 3 Thermal oxidative aging resistance and extraction resistance of styrene-butadiene rubber vulcanizate

[0167]

[0168] The embodiments listed above are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for preparing an alkenyl chitosan-based multifunctional macromolecular rubber antioxidant, characterized in that: The following steps are involved: (1) Dissolving chitosan in an acidic solvent, forming a salt with the amino groups on the chitosan, adding unsaturated fatty acids and / or unsaturated fatty acid halides, stirring and reacting at 0-80° C. for 6-36 hours, then adjusting the pH value of the reaction system to 8-10, filtering out the solid matter, purifying, and drying to obtain a chitosan derivative containing a double-bond hydrocarbon chain; (2) After swelling a chitosan derivative containing a double-bond hydrocarbon chain in a solvent, adding a small molecule antioxidant containing a carboxyl group, reacting at room temperature to 100° C. for 12 to 72 hours under the action of a condensing agent and a catalyst, purifying, and drying to obtain a chitosan-based multifunctional macromolecular rubber antioxidant with an alkenyl group; The acidic solvent in step (1) is at least one of methanesulfonic acid, ethanesulfonic acid, and methanesulfonic acid / dimethyl sulfoxide; the proton H + The molar ratio of the chain segments to the chitosan unit ring is ≥1; The proton H in the acidic solvent + The molar ratio of the chain segments to the chitosan unit ring is 1 to 22; The unsaturated fatty acid in step (1) is at least one of butenoic acid, pentenoic acid, octenic acid, undecenoic acid, hexadecenoic acid, octadecenoic acid, eicosenoic acid, linoleic acid, linolenic acid, palmitoleic acid and arachidonic acid; The unsaturated fatty acid halide in step (1) is at least one of crotonoyl halide, pentenoyl halide, octenoyl halide, undecenoyl halide, hexadecenoic acid halide, octadecenoic acid halide, eicosenoic acid halide, linoleic acid halide, linolenic acid halide and arachidonic acid halide; wherein the halogen is at least one of chlorine, bromine and iodine; The molar ratio of the unsaturated fatty acid and / or unsaturated fatty acid halide to the chitosan unit ring in step (1) is 0.5 to 3:1; The general structural formula of the carboxyl-containing small molecule antioxidant in step (2) is as follows: In the formula, R1, R2, R3, and R4 are at least one of tert-butyl, hydroxy, methoxy, methyl, and hydrogen, and at least one of R1, R2, R3, and R4 is a hydroxyl group; Where y is any number between 0 and 1; The molar ratio of the carboxyl-containing small molecule antioxidant to the chitosan derivative unit ring containing a double-bond hydrocarbon chain in step (2) is 1 to 5:

1.

2. The method for preparing a chitosan-based multifunctional macromolecular rubber antioxidant with alkenyl groups according to claim 1, characterized in that: The molar ratio of the condensing agent in step (2) to the small molecule antioxidant containing a carboxyl group is 1 to 3:1; the condensing agent is at least one of dicyclohexylcarbodiimide, diisopropylcarbodiimide, and 1-ethyl-(3-dimethylaminopropyl)carbodiimide; the molar ratio of the catalyst to the small molecule antioxidant containing a carboxyl group is 0.05 to 1:1; the catalyst is at least one of N-hydroxysuccinimide, 4-dimethylaminopyridine, and pyridine.

3. The method for preparing a chitosan-based multifunctional macromolecular rubber antioxidant with alkenyl groups according to claim 1, characterized in that: The pH value of the reaction system in step (1) is adjusted with an alkaline solution, wherein the alkaline solution is at least one of sodium hydroxide solution, potassium hydroxide solution, sodium carbonate solution, potassium carbonate solution, sodium bicarbonate solution, and potassium bicarbonate solution; The swelling temperature in step (2) is 50 to 120° C. and the swelling time is 12 to 96 hours; The solvent in step (2) is at least one of methanol, dimethyl sulfoxide, N,N-dimethylformamide, and N,N-dimethylacetamide; the mass ratio of the chitosan derivative containing a double-bond hydrocarbon chain to the solvent is 1g:20-120mL.

4. The method for preparing a chitosan-based multifunctional macromolecular rubber antioxidant with alkenyl groups according to claim 1, characterized in that: The general structural formula of the carboxyl-containing small molecule antioxidant (B) in step (2) is as follows: In the formula, R1, R2, R3, and R4 are at least one of tert-butyl, hydroxy, methoxy, methyl, and hydrogen, and at least one of R1, R2, R3, and R4 is a hydroxyl group; Where y is any number between 0 and 1; When y=1, the carboxyl-containing small molecule antioxidant is prepared by the following method: A carboxyl-containing compound is dissolved in a solvent, a base is added to form a salt of the carboxyl group, and then a phenolic compound containing an aldehyde group is added, and the reaction is carried out at room temperature to 80°C for 3 to 24 hours to generate a Schiff base compound, which is then reduced with a reducing agent, and the pH value of the system is adjusted to 3 to 5 with an acid, and then filtered, purified, and dried to obtain a small molecule antioxidant containing a carboxyl group. The structural formula of the carboxyl-containing compound is: The amino group can be located at one of the 2, 3, and 4 positions of the benzene ring; the phenolic compound containing an aldehyde group wherein R1, R2, R3, and R4 are at least one of tert-butyl, hydroxy, methoxy, methyl, and hydrogen, and at least one of R1, R2, R3, and R4 is a hydroxyl group; The molar ratio of the carboxyl-containing compound to the aldehyde-containing phenolic compound is 1 to 3:1; The base is at least one of sodium hydroxide and potassium hydroxide; the molar ratio of the base to the carboxyl group-containing compound is 1 to 1.5:1; The reducing agent is at least one of sodium borohydride, sodium cyanoborohydride, and lithium aluminum tetrahydride; the molar ratio of the reducing agent to the aldehyde-containing phenolic compound is 1 to 1.5:1; The reaction temperature of the reducing agent reduction is 0 to 10°C and the time is 2 to 10 hours; The acid is at least one of a hydrochloric acid solution and an acetic acid solution; the concentration of the hydrochloric acid solution is 10-36.5%, and the concentration of the acetic acid solution is 50-100%.

5. A chitosan-based multifunctional macromolecular rubber antioxidant with alkenyl groups prepared by the preparation method according to any one of claims 1 to 4.

6. Use of the alkenyl-containing chitosan-based multifunctional macromolecular rubber antioxidant according to claim 5 in the rubber field.

7. The use of an alkenyl chitosan-based multifunctional macromolecular rubber antioxidant in the rubber field according to claim 6, characterized in that: When the alkenyl-containing chitosan-based multifunctional macromolecular rubber antioxidant is used to prepare rubber products or rubber composite materials, the mass ratio of the alkenyl-containing chitosan-based multifunctional macromolecular rubber antioxidant to the rubber is 3 to 15:100.

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